The existing automatic wash unit for a full-automatic biochemical analyzer comprises a motor and multiple sets of cleaning needle components, at least one of which has a wipe nozzle. Driven by the motor, the wipe nozzle of the cleaning needle component gets access into the reaction cuvette while the reaction tray pauses, touches the bottom of the cuvette, and rises without the reaction cuvette after a rather short period of time, thereby fulfilling the cleaning of the reaction cuvette. However, this wash unit suffers from the following shortcomings. As there is no anticollision mechanism, the wipe nozzle may easily collide with the wall of the cuvette when it gets access into the reaction cuvette, thereby making the wipe nozzle, cleaning needles and the reaction cuvette damaged. Moreover, the existing structures are rather complicated. They either move unevenly, or fail to perform the power-off self-locking in the vertical direction, or are compromised by a high cost.